The present invention relates to a cathode ray tube phosphor screen inspecting method and apparatus for inspecting defects on a phosphor screen formed on the face inner surface of a panel of a cathode ray tube in the steps of manufacturing the cathode ray tube.
Conventionally, as shown in FIGS. 1A and 1B, a black film 12 having a predetermined pattern is formed on a face inner surface 11b of a curved glass face 11a forming a panel 11 of a cathode ray tube such as a display tube. As shown in FIGS. 2A to 2C, in the pattern of this black film 12 a large number of holes 13 having a predetermined shape such as a circular shape are regularly formed. In the steps of manufacturing a cathode ray tube, this pattern is formed on the face inner surface 11b through a resist coating step, an exposure step using a shadow mask, a development step using no shadow mask, and a dag coating step.
In this black film pattern formation process, as shown in FIGS. 2A to 2C, small-diameter holes P1, a deformed hole P2, no-aperture portions P3, and large-diameter holes (not shown) sometimes form as defects in the black film 12. That is, the small-diameter holes P1 shown in FIG. 2A are smaller than other holes 13 having a predetermined shape. The deformed hole P2 shown in FIG. 2B is different in shape from the circular holes 13. In the no-aperture portions P3 shown in FIG. 2C, no holes 13 are formed in portions where the apertures 13 are to be formed. The large-diameter holes are larger than other holes 13 having a predetermined shape.
Many of these small-diameter holes P1, deformed hole P2, and no-aperture portions P3 form in the exposure step. That is, exposure is performed via a shadow mask in the exposure step. Therefore, if the diameters of some holes in the shadow mask are smaller than the diameter of other normal holes, small-diameter holes P1 form as shown in FIG. 2A. Also, a fine dust particle sticking to the film surface forms a deformed hole P2 in which a part of an aperture hole 13 is missing, as shown in FIG. 2B. Furthermore, if the shadow mask is locally devoid of holes, no-aperture portions P3 form as shown in FIG. 2C. Since one of three dots of blue, green, and red phosphors is formed in each hole of the shadow mask, a defect involves a set of three holes as indicated by the alternate long and two dashed lines in FIGS. 2A and 2B.
After a defect-free black film 12 is formed, the film 12 is sequentially coated with blue, green, and red phosphors to form phosphor films, thereby finally forming a phosphor screen. The phosphor films are formed as follows. First, a phosphor is charged into the panel inner surface, and a phosphor film of the first color is formed through spin coating, drying, an exposure step using a shadow mask, and a development step using no shadow mask. After that, phosphor films of the second and third colors are formed through the same process.
In this phosphor film formation process, as shown in FIGS. 3A and 3B, phosphor films 14 of blue B, green G, and red R are sometimes not well formed to produce defects. A representative defect is called dot missing e.g. phosphor peeling. In FIG. 3A, a part of the phosphor film 14 of blue B is missing in the aperture 13 in the black film 12. In FIG. 3B, the phosphor film 14 of green G is entirely missing in the aperture 13 in the black film 12. In either case, phosphors failed to adhere in a desired pattern. Furthermore, in the phosphor film coating process, where dust adheres to the inner surface of the panel, the portions of which the phosphors are to be formed, are occupied with the dust. These portions are defect called dust.
Although either dot missing: described above is a defect, whether dot missing is non-defective (non-defective product) or defective (defective product) is in many instances determined in accordance with the position or pattern (defect pattern) on the phosphor screen. For example, it is very difficult to form a defect-free phosphor film in a display tube for use in a monitor display; some defects are practically no problem depending on the position or pattern on the phosphor screen.
Patterns of dot missing as a defect and a method of determining whether dot missing is non-defective or defective in accordance with the pattern will be described below with reference to FIGS. 4A to 7B.
FIGS. 4A and 4B show missing of a set of three dots of blue B, green G, and red R forming one pixel. In FIG. 4A, three dots of blue B, green G, and red R horizontally arranged in a line are missing. In FIG. 4B, three dots of blue B, green G, and red R adjacent to each other in the form of a triangle are missing. In either case, it is determined that the dot missing is non-defective if only one set of dots are missing and defective if two or more sets of dots are missing.
FIGS. 5A and 5B show missing of two adjacent dots of the same color. In FIG. 5A, two dots of blue B horizontally adjacent to each other are missing. In FIG. 5B, two dots of blue B adjacent to each other in different rows are missing. In either case, it is determined that the dot missing is defective.
FIGS. 6A and 6B show missing of two adjacent dots of two different colors. In FIG. 6A, two adjacent dots of blue B and green G are missing, and it is, for example, determined that this dot missing is defective. In FIG. 6B, two dots of blue B and green G at a distance d1 are missing. It is determined that this dot missing is non-defective if, for example, the distance d1 is 50 mm or more and defective if the distance d1 is 50 mm or less. Also, even when two dots of the same color are missing, it is determined that this dot missing is non-defective if the distance d1 is 50 mm or more.
FIGS. 7A and 7B show missing of one set of dots and another dot at a distance d2. It is determined that this dot missing is non-defective if, for example, the distance d2 is 50 mm or more and defective if the distance d2 is 50 mm or less.
FIG. 8 shows a method of determining whether dot missing is non-defective or defective in accordance with the position of the dot missing on an effective surface (phosphor screen) of the panel 11. Assume, for example, that a central circle on the effective surface of the panel 11 is a region A1 and its outside portion is a region A2. If this is the case, the region A1 is required to be defect-free, and the above defect standards are applied to the region A2.
These non-defectivexc2x7defective determination standards are sometimes changed in accordance with the type and size of display tube.
The quality of a phosphor screen on which a black film 12 and phosphor films 14 are thus formed is usually inspected at the exit of a black film coating machine or a phosphor screen coating machine. This inspection is manually performed by placing the panel 11 on a panel conveyor or unloading the panel 11 from the panel conveyor and placing the panel 11 on a light table.
In this inspection of the phosphor screen on which the black film 13 and the phosphor films 14 are formed, e.g., in inspection of the phosphor screen of a common display tube, however, searching for defects is time-consuming and difficult because the diameter of the apertures 13 in the black film 12 is 90 to 150 xcexcm and the aperture pitch of the apertures 13 for, e.g., green and green phosphors is 200 to 280 xcexcm, a very small value. Hence, inspecting display tubes that are becoming increasingly finer is a heavy burden on inspectors, so some improvements are being demanded.
It is an object of the present invention to provide a cathode ray tube phosphor screen inspecting method capable of automatically and accurately inspecting defects on the phosphor screen of a cathode ray tube.
It is another object of the present invention to provide a cathode ray tube phosphor screen inspecting apparatus capable of automatically and accurately inspecting defects on the phosphor screen of a cathode ray tube.
According to the present invention, there is provided a cathode ray tube phosphor screen inspecting method comprising the steps of illuminating a panel of a cathode ray tube, in which a phosphor screen having a regular pattern is formed on an inner surface of a face, from the inner surface of the face, imaging the face inner surface, and specifying a defect on the phosphor screen from data obtained by the imaging.
According to the present invention, there is provided a cathode ray tube phosphor screen inspecting method comprising the steps of illuminating a panel of a cathode ray tube, in which a phosphor screen having a regular pattern is formed on an inner surface of a face, from the inner surface or an outer surface of the face, imaging light components transmitted through the same position on the phosphor screen of the panel in a plurality of directions at the same time, moving imaging positions relative to the phosphor screen of the panel, and specifying a potential defective portion detected by the simultaneous imaging in a plurality of directions as a defect on the phosphor screen.
According to the present invention, there is provided a cathode ray tube phosphor screen inspecting method comprising the steps of illuminating a panel of a cathode ray tube, in which a phosphor screen having a regular pattern is formed on an inner surface of a face, from an outer surface of the face, imaging light transmitted through the panel, specifying a defect on the phosphor screen from data obtained by the imaging, and collating the specified defect on the phosphor screen with non-defectivexc2x7defective determination conditions defining non-defectivexc2x7defective of a position and pattern on a phosphor screen, thereby determining whether the phosphor screen is non-defective or defective.
According to the present invention, there is provided a cathode ray tube phosphor screen inspecting apparatus comprising illuminating means for illuminating a panel of a cathode ray tube, in which a phosphor screen having a regular pattern is formed on an inner surface of a face, from the inner surface of the face, imaging means for imaging the face inner surface, and defect detecting means for specifying a defect on the phosphor screen from imaging data obtained by the imaging means.
According to the present invention, there is provided a cathode ray tube phosphor screen inspecting apparatus comprising illuminating means for illuminating a panel of a cathode ray tube, in which a phosphor screen having a regular pattern is formed on an inner surface of a face, from the inner surface or an outer surface of the face, a plurality of imaging means for imaging light components transmitted through the same position on the phosphor screen of the panel in a plurality of directions at the same time, moving means for moving imaging positions relative to the phosphor screen of the panel, and defect detecting means for specifying a potential defective portion detected by the simultaneous imaging in a plurality of directions as a defect on the phosphor screen.
According to the present invention, there is provided a cathode ray tube phosphor screen inspecting apparatus comprising illuminating means for illuminating a panel of a cathode ray tube, in which a phosphor screen having a regular pattern is formed on an inner surface of a face, from an outer surface of the face, imaging means for imaging light transmitted through the panel, defect detecting means for specifying a defect on the phosphor screen from imaging data obtained by the imaging means, storage means for storing non-defectivexc2x7defective determination conditions defining non-defectivexc2x7defective of a position and pattern of a defect on a phosphor screen, and non-defectivexc2x7defective determining means for collating the defect specified on the phosphor screen by the defect detecting means with the non-defectivexc2x7defective determination conditions stored in the storage means, thereby determining whether the phosphor screen is non-defective or defective.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.